The present invention relates to a defect inspection apparatus and a defect inspection method for inspecting defects in a repeated pattern in an image device or a memory device, or for inspecting defects in a repeated pattern on a photomask used to form the pattern on an image device or a memory device. The present invention also relates to a method of manufacturing a photomask using such a defect inspection apparatus and a defect inspection method. The present invention further relates to a pattern transferring method using such a photomask and to a semiconductor wafer manufacturing method using such a photomask or a defect inspection method.
Conventionally, a defect inspection has been conducted as one of inspection items to inspect patterns formed on the surfaces of an image device such as an imaging device or a display device, or of a photomask used for manufacturing the image device. For example, there may occur an error in which patterns having different regularity are unintentionally included in patterns which otherwise should be arranged in uniform regularity. Such error is sometimes referred to as an irregularity defect. This kind of defects is caused by some or other reasons in the manufacturing process.
The presence of an irregularity defect in an imaging device or a display device may induce irregularity in sensitivity or display, which may lead to deterioration of device performance. Also, if an irregularity defect is present in a pattern of a photomask used for manufacturing an image device such as an imaging device or a display device, the irregularity defect will be transferred to the pattern of the image device, which may lead to deterioration of performance of the image device.
According to conventional techniques, such irregularity defect in patterns on image devices or photomasks often cannot be detected by shape inspection of individual patterns for the reason that micro defects are usually arranged regularly. However, when the defective region is viewed as a whole, it looks different from other normal regions. Therefore, the irregularity defect inspection is principally conducted visually by an operator using an oblique viewing inspection method or the like.
However, such visual inspection involves a problem that inspection results vary depending on the operator. Therefore, there is a demand for an automated irregularity defect inspection apparatus capable of performing an irregularity defect inspection automatically.
A macro inspection apparatus for semiconductor wafers is one of such apparatuses designed to automate the oblique viewing inspection. For example, Japanese Unexamined Patent Application Publication (JP-A) No. H09-329555 (hereafter referred to as Patent Document 1) discloses a macro inspection apparatus which includes a light source for applying light with a desired wavelength to a periodic structure on a semiconductor wafer, a camera for receiving diffracted light from the substrate surface, and detection means for detecting a defect by comparing image data taken by the camera with reference image data involving no defect. This macro inspection apparatus is designed to inspect the entire surface of a wafer with a single field of view to detect focus offset, defocus caused by the wafer position being vertically shifted due to presence of dust (particles) under the wafer, and surface defects in the semiconductor wafer structure arising in the development, etching, and release processes of the wafer. When inspecting a semiconductor wafer that is an object to be inspected having a periodic structure (a repeated pattern 151 having unit patterns 153 arranged regularly) as shown in FIG. 5 by the defect inspection using diffracted light as disclosed in Patent Document 1, the diffraction formulad(sin θm±sin θi)=mλ  (1)can be used when a pitch of the periodic structure is denoted by d, the incidence angle is denoted by θi, the diffraction angle when the order of diffracted light is m is denoted by θm, and the wavelength of incident light is denoted by λ. However, since zeroth order diffracted light (direct light) contains no micro defect information, the order of diffracted light should be of an absolute value greater than zero in order to obtain micro defect information. As seen from the formula (1) above, the diffraction order and the diffraction angle vary depending on the pitch of the periodic structure.
According to the description of Patent Document 1, the direction of diffracted light and the wavelength of incident light are changed to obtain first-order diffracted light according to the range of pitches of 0.6 μm to 4 μm given in the design rule currently applied to semiconductor wafers. As a specific method for changing the diffraction angle, Patent Document 1 also discloses provision of a camera installed at several different angles.
However, when a wafer surface is viewed from an oblique direction by changing the angle of a camera serving as an observation apparatus as described in Patent Document 1, the distance between the camera object lens and the object is not uniform. This induces a problem that the resulting image of the surface has perspective, whereby the image of a repeated pattern which is originally supposed to have uniform dimensions are made ununiform or the focus is deviated in the surface. As a result, it is required to correct the perspective by image processing or the like, and such processing is complicated. In order to enable correct observation of irregularity without using such complicated processing, it is most desirable to arrange the light-receiving optical system of the observation apparatus directly above an object to be inspected so that the light-receiving optical system can receive light that is generated perpendicularly from the surface of the object to be inspected when irradiated with light from the light source apparatus.
However, as shown in FIG. 6, when an observation apparatus 113 is arranged directly above an object to be inspected 150, and incident light (incident light Ri when detecting reflected light, or incident light Ri′ when detecting transmitted light) is applied to the object to be inspected 150 from a light source (a light source 112 when detecting reflected light, or a light source 112′ when detecting transmitted light), the object lens (not shown) of the observation apparatus 113 will capture not only n-order diffracted light Rm (the absolute value of n is greater than zero) but also zeroth order diffracted light R0 including no defect information that is reflected or transmitted at an zeroth order diffraction angle θ0 that is the same angle as an incidence angle θi, if the incidence angle θi is small, depending on an irradiated region (an irradiated region A when detecting reflected light, or an irradiated region A′ when detecting transmitted light) that is defined by the spot diameter of the light source 112 or 112′, a distance B between the object to be inspected 150 and the object lens of the observation apparatus 113 that is determined by focus control when a camera is used to capture an image of the object to be inspected, and the diameter D of the object lens of the observation apparatus 113. As a result, a large amount of light including no defect information is contained in the light captured by the observation apparatus 113, resulting in deterioration of contrast in defect information.
In contrast, if a light source apparatus is arranged at a position where the light from the light source apparatus is incident at a relatively large incidence angle, the observation apparatus will capture diffracted light having an order the absolute value of which is even higher as seen from the formula (1). Although the diffracted light having an order the absolute value of which is high is advantageous in capturing fine structures, the light quantity is reduced as the absolute value of the order becomes higher, as shown in FIG. 7. In this case, the sensitivity of the camera tends to be insufficient, inducing a problem of difficulty to observe defects.
Moreover, the inspection must support a very wide range of pixel pitches. For example, when the inspection is conducted on a display device such as a liquid-crystal panel or large-sized photomask used for manufacture of such device, the inspection must support pixel pitches ranging from 50 to 800 μm. When the object to be inspected is a semiconductor wafer for use in an imaging device such as CCD, the pixel pitch ranges from 0.5 to 8 μm, and when the object to be inspected is a photomask used in manufacture of a semiconductor wafer for an imaging device such as CCD, the pixel pitch ranges from 8 to 50 μm. As the pitch d of a repeated pattern becomes greater, the absolute value of the order of the diffracted light becomes higher. Therefore, even if the incidence angle is set to a minimum possible value at which no zeroth order diffracted light is captured, the absolute value of the order of the diffracted light becomes so high that the quantity of light becomes insufficient to detect irregularity. Further, the light quantity of the diffracted light is varied not only depending on the pitch d of the repeated pattern but also depending on an edge-to-edge width a of the repeated pattern (see FIG. 5). Therefore, it is possible that the light quantity becomes insufficient depending the edge-to-edge width a of the object to be inspected.
The insufficient light quantity may be complemented by a method of highlighting a defect by performing image processing such as highlight processing on an image captured by a camera having insufficient sensitivity. In this case, however, irregularities attributable to the camera itself are also captured, which is not desirable.